If you surf the Apple store (when it's up), the MacBook Pros will typically have time clocks for certain tasks, and they compare them to the previous model.
The difference is in the efficiency of a processor. A single core processor with one thread running at 2.7 Ghz is fast, but a dual or quad core processor is much more efficient.
The best analogy I've heard for cores/threads in processors is it's like waiting in line to buy something with checkout lanes. Older processors would simply have one giant line with a really fast cashier on it. Newer processors spread out their workload, akin to opening up more checkout lanes. So while your older computer is pretty fast at checking out one person at a time, newer computers are perhaps slightly slower but they're getting multiple people through the line at the same time.